VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur

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1 VALLIAMMAI ENGINEERING COLLEGE SRM Nagar, Kattankulathur DEPARTMENT OF COMPUTER SCIENCE ENGINEERING SUBJECT QUESTION BANK : MA6566 \ DISCRETE MATHEMATICS SEM / YEAR: V / III year CSE. UNIT I - LOGIC AND PROOFS Propositional Logic Propositional equivalences - Predicates and Quantifiers Nested Quantifiers Rules of inference - Introduction to proofs Proof methods and strategy. Q.No. Question Bloom s Taxonomy Level PART A Domain 1. Construct the truth table for the compound proposition (p q) ( p q). 2. Construct the truth table for the compound proposition (p q) (q p). 3. What are the contrapositive, the converse and the inverse of the conditional statement If you work hard then you will be rewarded. 4. Find the truth table for the statement p q. 5. Give the truth value of T T F. 6. Write the symbolic representation of If it rains today, then I buy an umbrella. 7. When do you say that two compound propositions are equivalent? 1

2 8. Show that ( p r) (q r)and (p q) r are logically equivalent. 9. Show that the propositions p q and p q are logically equivalent. 10. Without using truth table show that p (q p) p (p q). 11. Show that (p (q r)) ((p q) (p r)) is a tautology. 12. Is p (p q)) q a tautology? 13. Using the truth table, show that the proposition p (p q) is a tautology. 14. Given P = {2,3,4,5,6}, state the truth value of the statement ( x p)(x + 3 = 10 ). 15. Let E = { 1,0,1,2} denote the universe of discourse. If P(x, y) = x + y + 1, find the truth value of ( x)( y)p(x, y). Find a counter example, if possible, to these universally quantified statements, Whose the universe of discourse for all variables consists of all integers. 16. (a) x y (x 2 = y 2 x = y). (b) x y (xy x). 17. What are the negations of the statements x (x 2 > x) and x (x 2 = 2)? 18. Write the negation of the statement ( x)( y)p(x, y). 19. Give an indirect proof of the theorem If 3n + 2 is odd, then n is odd. 20. Prove that p, p q, q r r 2

3 PART B 1.(a) Prove that ((p q) ( p ( q r))) ( p q) ( p r) is a tautology 1. (b) Show that (p q) (r s), (q t) (s u), (t u)and (p r) p) 2. (a) Determine whether ( p (p q)) q is a tautology. 2.(b) 3. (a) Show that ( x)(p(x) Q(x)) ( x)p(x) ( x)q(x). Is the converse true? Show that x(p(x) Q(x)) xp(x) xq(x) 3.(b) 4. (a) Write the symbolic form and negate the following statements. 1. Everyone who is healthy can do all kinds of work. 2. Some people are not admired by everyone. 3. Everyone should help his neighbors or his neighbors will not help him. 4. Everyone agrees with someone and someone agrees with everyone Without constructing the truth tables, obtain the principle disjunctive normal form of ( p r) (q r) 4.(b) Show that r s can be derived from the premises p (q s), r p and q 5. (a) Establish this logical equivalences, where A is a proposition not involving any quantifiers. Show that ( xp(x)) A x(p(x) 5.(b) 6.(a) A)and ( xp(x)) A x(p(x) A) Show that xp(x) x Q(x) and x(p(x) Q(x)) are not logically equivalent Use the quantifiers and predicates to express the fact that lim x a f(x) does not exist. 6.(b) Show that xp(x) x Q(x) is equivalent to x y (P(x) Q(y)) 3

4 7. (a) 7. (b) Show that the hypothesis, It is not sunny this afternoon and it is colder than yesterday. We will go swimming only if it is sunny, If do not go swimming then we will take a canoe trip and If we take a canoe trip, then we will be home by sunset. Lead to the conclusion we will be home by sunset. Prove that 2 is irrational by giving a proof by contradiction. 8. (a) Prove that ( x)(p(x) q(x) x p(x) x q(x) 8.(b) 9. (a) Prove that (P Q) (R Q) (P R) Q) Show that x(p(x) Q(x)) xp(x) xq(x) by indirect method. 9.(b) Show that the statement Every positive integer is the sum of squares of three integers is false. 10.(a) Using indirect method of proof, derive P S from the premises P (Q R), Q P, S R and P. 10.(b) Without using truth table find PCNF and PDNF of P (Q P) ( P ( Q R)). 11. (a) Prove that the premises P Q, Q R, R S, S R and P S are inconsistent. 11. (b) Show that the premises One student in this class knows how to write program in JAVA, and Everyone who knows how to write the programme in JAVA can get a high paying job imply a conclusion someone in this class can get a high paying job. 12. (a) Show that ( P R) (Q P) = (P Q R) (P Q R) (P Q R) ( P Q R) ( P Q R). 12. (b) Use the quantifiers to express following statements. 1. there is a student in the class who can speak Hindi.2.every student in this class knows how to drive a car.3.some student in this class knows has visited Alaska but not visited Hawaii.4.all students in this class have learned at least one programming language. 13. (a) Prove that of (P Q) (Q R) (P R). 4

5 13.(b) Prove that A D is a conclusion from the premises A B C, B A and D C by using conditional proof. 14. (a) State and explain the proof methods. 14. (b) Show that that x P(x) x Q(x) x (P(x) Q(x)) UNIT II -COMBINATORICS Mathematical induction Strong induction and well ordering The basics of counting The pigeonhole principle Permutations and combinations Recurrence relations Solving linear recurrence relations Generating functions Inclusion and exclusion principle and its applications. Bloom s Q.No. Question Taxonomy Level Domain 1. State the principle of strong induction. 2 Use mathematical induction to show that n = n(n+1) 2 3 Use mathematical induction to show that n! 2 n+1, n = 1,2,3, 4 What is well ordering principle? 5 How many permutations are there in the word MISSISSIPPI? 6 State the Pigeonhole principle. 7 What is the number of arrangements of all the six letters in the word PEPPER? 8 How many permutations of {a,b,c,d,e,f,g} starting with a? 9 In how many ways can all the letters in MATHEMATICAL be arranged? 10 How many ways can a 2xn rectangular board be tiled using 1x2 and 2x2 pieces? 11 How many different bit strings are there of length seven? 5

6 Twelve students want to place order of different ice creams in a ice cream 12 parlor, which has six type of ice creams. Find the number of orders that the twelve students can place. 13 How many permutations are there in the word SACHIN? 14 Find the recurrence relation for the Fibonacci sequence. 15 Find the recurrence relation satisfying the equation y n = A(3) n + B( 4) n 16 Solve the recurrence relation y(k) 8y(k 1) + 16y(k 2) = 0, k 2, where y(2) = 16 and y(3) = Write the generating function for the sequence 1, a, a 2, a 3, 18 Find the number of non-negative integer solutions of the equation x 1 + x 2 + x 3 = 11 Determine whether the sequence {a 19 n } is a solution of the recurrence relation a n = 2a n 1 a n 2, n=2, 3, 4, where a n = 3n for every non negative integer n. 20 What is the solution of the recurrence relation a n = 6a n 1 9a n 2 with a 0 = 1, a 1 = 6 PART-B 1.(a) Using induction principle prove that n 3 + 2n is divisible by (b) 2. (a) Show that if n and k are positive integers then ( n+1 n ) = (n + 1)( k k 1 ) k. Use this identity to construct an inductive definition of the binomial coefficient. Prove that in a group of six people, at least three must be mutual friends or at least three must be mutual strangers. 2.(b) 3. (a) 3.(b) From a club consisting of six men and seven women, in how many ways we select a committee of (1) 3 men and 4 women? (2) 4 persons which has at least one woman? (3) 4 persons that has at most one man? (4) 4 persons that has both sexes? There are three files of identical red, blue and green balls, where each files contains at least 10 balls. In how many ways can 10 balls be selected. (1) If there is no restriction. (2) If at least 1 red ball must be selected. (3) If at least 1 red, at least 2 blue and at least 3green balls must be selected. (4) If at most 1 red ball is selected. Prove by mathematical induction that n 2 = n(n+1)(2n+1) 6 6

7 4. (a) State the strong induction (the second principle of mathematical induction). Prove that a positive integer >1 is either a prime number or it can be written as product of prime numbers. 4.(b) 5. (a) 5.(b) 6. (a) If n pigeonholes are occupied by (kn+1) pigeons, where k is a positive integer, prove that at least one pigeonhole is occupied by (k+1) or more pigeons. Hence, find the minimum number of m integers to be selected from S = {1, 2,3 9} so that the sum of two of m integers is even. Use mathematical induction to show that n > n, n 2 Find the number of integers between 1 and 250 both inclusive that are not divisible by any of the integers 2, 3, 5 and 7. Use the principle of inclusion exclusion to derive a formula for φ(n) when the prime factorization of n is n = p 1 α 1 p 2 α 2 p m α m 6.(b) A total of 1232 students have taken a course in Spanish, 879 have taken a course in French and 114 have taken a course in Russian. Further 103 have taken courses in both Spanish and French, 23 have taken courses in both Spanish and Russian and 14 have taken courses in both French and Russian. If 2092 students have taken at least one Spanish, French and Russian, how students have taken a course in all three languages? 7. (a) Let m be any odd positive integer. Then prove that there exist a positive integer n such that m divides 2 n 1 7. (b) Determine the number of positive integer n, 1 n 2000 that are not divisible by 2, 3 or 5 but are divisible by (a) Prove by mathematical induction that 6 n n+1 is divisible by 43, for each positive integer n. 8.(b) Prove that the number of subsets of a set having n elements is 2 n 9.(a) Solve the recurrence relation a n = 3a n 1 3a n 2 a n 3 with a 0 = 5, a 1 = 9 and a 2 = (b) Find the solution to the recurrence relation a n = 6a n 1 11a n 2 + 6a n 3 with initial conditions a 0 = 2, a 1 = 5 and a 2 = 15 7

8 10.(a) Solve the recurrence relation a n+1 a n = 3n 2 n, n 0, a 0 = 3 10.(b) Use the method of generating function to solve the recurrence relation a n = 4a n 1 4a n n ; n 2 given that a 0 = 2 and a 1 = (a) 11.(b) 12.(a) 12.(b) 13.(a) 13.(b) 14.(a) 14.(b) Solve the recurrence relation a n = 3a n 1 3a n 2 a n 3 given that a 0 = 5, a 1 = 9 and a 2 = 15 Solve the recurrence relation a n = 3a n 1 + 2, n 1, with a 0 = 1 by the method of generating function. Use the method of generating function to solve the recurrence relation a n = 3a n 1 + 1, n 1, with a 0 = 1 Use the method of generating function to solve the recurrence relation a n 5a n 1 + 6a n 2 = 0, where n 2, a 0 = 0, a 1 = 1 Use the method of generating function to solve the recurrence relation a n + 3a n 1 4a n 2 = 0, where n 2, a 0 = 3, a 1 = 2 Find the generating function of Fibonacci sequence. A factory makes custom sports cars at an increasing rate. In the 1 st Month only one car made, in the 2 nd month two cars are made, and so on with n cars made in the n th month.(1) Set up the recurrence relation for the number of cars produced in the first n month by this factory. (2) How many cars are produced in the 1 st year? Find all solutions of the recurrence relation a n = 2a n 1 + 2n 2 UNIT III -GRAPHS Graphs and graph models Graph terminology and special types of graphs Matrix representation of graphs and graph isomorphism Connectivity Euler and Hamilton paths. Q.No. Question Bloom s Taxonomy Level Domain PART - A 1. Define complete graph and give an example. 2. Define a regular graph. Can a complete graph be a regular graph? 8

9 3. How many edges are there in a graph with 10 vertices each of degree 6? 4. Define pseudo graphs. 5. Define strongly connected graph. 6. State the handshaking theorem. 7. Prove that the number of odd degree vertices is always even. Represent the given graph using an adjacency matrix Define isomorphism of two graphs. 10. Define connected graph and a disconnected graph with example. 11. Define pendant vertex in a graph. 12. How many edges does a graph have if it has vertices of degree 5, 2, 2, 2, 2, 1? Draw such a graph. Use an incidence matrix represents the graph Define Eular line, Eular graph. 15. Define a Hamilton path of G. 16. What should be the degree of each vertex of a graph G if it has Hamilton circuit? 17. Give an example of a non- Eulerian graph which is Hamiltonian. 18. State the necessary and sufficient conditions for the existence of an Eulerian path in a connected graph. 9

10 19. For which values of n do the graphs K n and C n have an Euler path but no Euler circuit? Does the graph have a Hamilton path? If so find such a path (a) Prove that the number of vertices of odd degree in a graph is always even. 1. (b) Prove that the maximum number of edges in a simple disconnected graph G with n vertices and k components is (n k)(n k 1) 2 2. (a) Prove that a connected graph G is Euler graph if and only if every vertex of G is of even degree. Consider the graph in the following figure. Find the path, simple path, circuit and cycle. 2.(b) 3. (a) Examine whether the following pair of graphs are isomorphic or not. Justify your answer. 10

11 Let δ(g)and (G) denotes minimum and maximum degrees of all 3.(b) the vertices of G respectively. Then show that for a non-directed graph G, δ(g) 2 E (G) V 4. (a) Let G be a graph with n vertices and n edges such that the vertices have K or K + 1, prove that if G has N k vertices of degree K and N k+1 vertices of degree K + 1 then N k = (K + 1)n 2n 4.(b) 5. (a) 5.(b) 6. (a) Show that isomorphism of that simple graphs is an equivalence relation. For any simple graph G, the number of edges of G is less than or equal to n(n 1), where n is the number of vertices in G. 2 Derive a connected graph has an Euler trail if and only if it has at most two vertices of odd degree. Prove that any undirected graph has an even number of vertices of odd degree. Show that the following graphs G and H are not isomorphic. 6.(b) 7. (a) Define 1. Adjacency matrix. 2. Incidence matrix of a graph with example. 11

12 7. (b) A simple graph with n vertices (n 3) in which each vertex has degree at least n 2 (δ n 2 ) has a Hamiltonian cycle. 8. (a) Define 1. Complete graph. 2. Complete bipartite graph with example. 8.(b) Show that the following graphs are isomorphic. 9. (a) Define 1. Euler graph 2. Hamiltonian graph with example. 9.(b) How many paths of length four are there from a to d in the simple graph G given below. 10.(a) Show that the complete graph K n contain n(n 1) different Hamilton cycle (b) Briefly explain about sub graph with example. 11.(a) Using adjacency matrix examine whether the following pairs of graphs G and G 1 given below are isomorphism or not. 12

13 11.(b) Briefly explain about walks with example. 12.(a) 12.(b) Draw the complete graph K 5 with vertices A, B, C, D, E. Draw all complete sub graph of K 5 with 4 vertices. The adjacency matrices of two pairs of graph as given below. Examine the isomorphism of G and H by finding a permutation matrix. A G = [ 0 0 1] A H = [ 1 0 0] (a) The sum of all vertex degree is equal to twice the number of edges (or) the sum of the degrees of the vertices of G is even. 13.(b) Write the adjacency matrix of the digraph G = { (v 1, v 3 ), (v 1, v 2 ), (v 2, v 4 ), (v 3, v 1 ), (v 2, v 3 ), (v 3, v 4 ), (v 4, v 1 ), }. (v 4, v 2 ), (v 4, v 3 ) Also draw the graph 14.(a) Prove that the following statements are equivalent for a simple connected graph.1.g is Eulerian. 2. Every vertex of G has even degree. 14.(b) Explain cut edges and cut vertices with suitable example. UNIT -IV ALGEBRAIC STRUCTURES Algebraic systems Semi groups and monoids - Groups Subgroups Homomorphism s Normal Subgroup and cosets Lagrange s theorem Definitions and examples of Rings and Fields. Q.No. Question Bloom s Domain Taxonomy Level PART - A 1. Define semigroup and monoid. Give an example of a semigroup which is not a monoid. 2. Give an example of sub semigroup. 3. Show that semi-group homomorphism preserves the property of idempotency. 13

14 4. What do you call a homomorphism of a semi-group into itself. 5. Prove that identity element in a group is unique Prove that monoid homomorphism preserves invertibility. State any two properties of a group. What is a group (G, ) called abelian? 9. Prove that if G is abelian group, then for all a, b G, (a b) 2 = a 2 b Show that every cyclic group is abelian. Prove or disprove: Every subgroup of an abelian is normal. 12. If a is a generator of a cyclic group G, then show that a 1 is also a generator of G. 13. Show that (Z 5, + 5 ) is a cyclic group. 14. Find the left cosets of {[0], [3]} in the addition modulo group (Z 6, + 6 ). 15. Define kernel of a homomorphism. 16. State Lagrange s theorem. 17. Define a ring. 18. Define a commutative ring. 19. Give an example of a ring which is not a field. 20. Define integral domain and give an example. 1.(a) Show that group homomorphism preserves identity, inverse, and sub group 1.(b) 2.(a) 2.(b) Obtain all the elements of (S 3, )and also construct the composition table with respect with respect to the operation. Prove that the intersection of two subgroups of a group G is again a subgroup of G Let G be a group and a G. Let f: G G be given by f(x) = axa 1, x G. Prove that f is an isomorphism of 14

15 3.(a) 3.(b) 4. (a) G onto G Show that M 2, the set of all 2X2 non singular matrices over R is a group under usual matrix multiplication. Is it abelian. Show that the union of two subgroups of a group G is again a subgroup of G if and only if one is contained in the other. State and prove Lagrange s theorem 4.(b) 5. (a) If S = NXN, the set of ordered pairs of positive integers with the operation defined by (a, b) (c, d) = (ad + bc, bd) and if f: (S, ) (Q, +) is defined by f(a, b) = a b, show that f is a semi group homomorphism. Prove that the intersection of two submonoids of a monoid is a monoid. 5.(b) Determine whether subgroups of Z 15. H 1 = {0, 5, 10} and H 2 = {0, 4, 8, 12} are 6. (a) Discuss Ring and Fields with suitable examples. 6.(b) State and prove the fundamental theorem of group homomorphism 7. (a) If G is an infinite cyclic group, then it is isomorphic to the additive group of integers. 7. (b) If G is a group of prime order, then G has no proper subgroups. 8. (a) Prove that the necessary and sufficient condition for a non-empty subset H of a group (G, )to be a subgroup is a, b H a b 1 H 8.(b) Let f: G, ) (H, ) be group homomorphism then show that Ker(f) is a normal subgroup. 9. (a) If f: G G is a group homomorphism then prove that f(a 1 ) = [f(a)] 1 9.(b) If (G, ) is an abelian group and if a, b G. Show that (a b) n = a n b n, for every integer n 10.(a) Define a cyclic group. Prove that any group of prime order is cyclic. 15

16 10.(b) 11.(a) 11.(b) 12.(a) 12.(b) Let (H, )be a subgroup of (G, ). Let N = {x /x G, xhx 1 = H}. Show that (N, ) is a subgroup of G. Prove that in a group G the equations a x = b and y a = b have unique solutions for the unknowns x and y as x = a 1 b, y = b a 1 when a, b G. Prove that the set of all matrices [ a b ]forms an abelian group b a with respect to matrix multiplication. If f: G G be a group homomorphism and H is a subgroup of G, then f 1 (H) is a subgroup of G Show that the set of all positive real numbers forms an group under the composition defined as a b = ab 4, a, b Q + 13.(a) Show that the group ({1, 2, 3, 4}, X 5 ) is cyclic. 13.(b) 14.(a) Prove that the order of an element a of a group G is the same as that of its inverse (a 1 ) Prove that the set {1, 1, i, i} is a finite abelian group with respect to the multiplication of complex numbers. 14.(b) State and prove Cayleys theorem. UNIT-V LATTICES AND BOOLEAN ALGEBRA Partial ordering Posets Lattices as posets Properties of lattices - Lattices as algebraic systems Sub lattices Direct product and homomorphism Some special lattices Boolean algebra. Q.No. Question Bloom s Taxonomy Level 1. Draw a Hasse diagram of X, where X = {2,4, 5, 10, 12, 20, 25} and relation be such that x y if x divides y 2. Show that the least upper bound of a subset B in a poset A, is unique if it exists. 3. Let A = {a, b, c} and ρ(a) be its power set, draw a Hasse diagram of ρ(a),. 4. State distributive lattice. 16

17 5. Check whether the posets {(1, 3, 6, 9), D} and {(1, 5, 25, 125), D}are lattices or not. Justify your claim. 6. Define lattice. Give suitable example. 7. Define sub lattice Define lattice homomorphism. Give an example of a lattice that is not complemented. In a lattice (L, ), prove that a (a b) = a, a, b L When is a lattice called complete? Give an example of a distributive lattice but not complete. Define Boolean Algebra. Show that in a Boolean Algebra ab + a b = 0 iff a = b 15. Prove the Boolean identity a. b + a. b = a Is a Boolean Algebra contains six elements? Justify your answer. What values of the Boolean variables x and y satisfy xy = x + y? 18. Is there a Boolean Algebra with five elements? Justify your answer. Find the values, if any, of the Boolean variable x that satisfy x. 1 = How many different Boolean functions are there of degree 7? 1.(a) Let D 30 = {1, 2, 3,5, 6, 10, 15, 30} and let the relation R be divisor on D 30. Find (1) All the lower bounds of 10 and 15. (2) The greatest lower bounds of 10 and 15. (3) All the upper bounds of 10 and 15. (4) The least upper bounds of 10 and 15. (5) Draw the Hasse diagram. 1. (b) Prove that in a Boolean Algebra(a b) = a b. 17

18 2. (a) Examine whether the lattice given in the following Hasse diagram is distributive or not? 2.(b) If P(S) is the power set of a non-empty set S, prove that {P(S),,,\, φ, S} is a Boolean Algebra. 3. (a) If S n is the set of all divisors of the positive integer n and D is the relation of division, prove that {S 30, D} is a lattice. Find also all the sub lattices of {S 30, D} that contain six or more elements. 3.(b) 4. (a) Show that every chain is a distributive lattice. State and prove De Morgan s law in a complemented distributive lattice. 4.(b) 5. (a) If a, b S, S = {1, 2, 3, 6} and a + b = LCM (a, b), a. b = GCD (a, b) and a = b a, show that {s, +,,, 1, 6} is a Boolean Algebra. Show that a complemented, distributive lattice is a Boolean Algebra. 5.(b) 6. (a) Show that De Morgan s laws hold in a Boolean Algebra that is show that for all x and y, (x ) y = x y and (x ) y = x y Show that every non empty subset of a lattice has a least upper bound and a greatest lower bound. 6.(b) Show that every totally ordered set is a lattice. 7. (a) Show that in a lattice if a b c, then (1) (a b) = b c and (2) (a b) (b c) = b = (a b) (a c). 18

19 7. (b) Show that in a Boolean algebra x x = x and x x = x 8. (a) Show that a lattice homomorphism on a Boolean Algebra which preserves 0 and 1 is a Boolean homomorphism. 8.(b) In a Boolean Algebra. Show that (a + b )(b + c )(c + a ) = (a + b)(b + c)(c + a) 9. (a) Let L be a lattice, where a b = glb(a, b), a b = lub(a, b), a, b L. Then both binary operators and defined as in L satisfy commutative law, associative law, absorption law and idempotent law. 9.(b) Show that in a distributive and complemented lattice satisfied De Morgan s law. 10.(a) Show that every chain is a lattice. 10.(b) 11.(a) Show that in a distributive and complemented lattice a b a b = 0 a b = 1 b a If P(S) is the power set of a set S and, are taken as join and meet, prove that P(S), is a lattice. Also, prove that the modular inequality of a lattice (L, ), For anya, b, c L, a c a (b c) (a b) c. 11.(b) In any Boolean algebra, show that ab + a b = 0 iff a = b. 12.(a) 12.(b) 13.(a) 13.(b) Prove that De Morgan s laws hold good for a complemented distributive lattice L,,, (a b) = a b and (a b) = a b In any Boolean algebra, prove that the following statements are equivalent: 1. a + b = b 2. a. b = a 3. a + b = 1 4. a. b = 0 Show that in a lattice if a b and c d, Then a c b d and a c b d. In a distributive lattice prove that a b = a c and a b = a c Imply b = c. 14.(a) Show that the distributive law x(y + z) = xy + xz is valid. 14.(b) Prove the absorption law x(x + y) = x using the the identities of Boolean algebra. 19

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